(A) Analysis of Wnt and frizzled gene expression in fetal hematopoietic tissues. Reverse transcription was performed with (+) or without (−) the addition of reverse transcriptase. PCR was performed on cDNAs from day-11 visceral yolk sacs (ys), day-14 fetal liver (fl), fetal liver AA4⁻ cells (flAA4⁻), fetal liver AA4⁺ cells (flAA4⁺), fetal liver AA4⁺ Sca⁺ c-kit⁺ cells (flASK), and day-14 fetal heads (fhd). Equal quantities of template were used for the PCR analysis of each cell population or tissue. The primer sets for amplification span known intron sequences of Wnt-3a³⁴ and Wnt-10b (GenBank accession no. MMU30464, MMWNT10B2⁶¹). The primer sets for Wnt-5a span introns found in the human gene.40 The genomic structures of the murine frizzled homologs Mfz3-7 are not known. In all reactions, no products were observed when reverse transcriptase was omitted.

(B) Analysis of frizzled gene expression in bone marrow and adult hematopoietic tissues. Reverse transcription was performed with or without the presence of RNase. PCR was performed on cDNAs from bone marrow mononuclear cells (BMMNC); AA4⁺ cells from the fetal liver, spleen, and thymus; and two independent samples of Lin^lo Sca⁺ cells from bone marrow. Equal quantities of template were used for all reactions. The primer sets for amplification were the same as in (A). Transcripts were detected for frizzled 3 and 7, with no expression detected for frizzled 5 and 4 (data not shown for frizzled 4). No expression of Wnt 3a, 5a, and 10b was detected in these samples.